In the book "Creatures of the North", you will find Scythe's handwriting in the book saying, "They should have faded in the centuries like I have.... Unless something else is keeping them in this world." You can find this book upon your entrance to the Northern Wastes Foothill, you can also find it in a house in Snowspire.

Summoners are one of the few enemies in game that do not fall over after a Flourish or Powerful spell.

Jack of Blades is insinuated to be the one that binds the Summoners to the world.

Once a summoner has taken enough damage to be killed, they will fall to their knees and send off one final shock wave that can bring a hero's combat multiplier down to zero. Make sure to stand clear or you will get very little XP from fighting them!

Summoners are in no way related to what their names imply; they obtained their name from their nature of summoning themselves due to the fact that their origin was from a powerful wizard that was cast out for using dangerous dark magic.